The present invention relates to resin parts for use in a mechanical transmission such as gears, friction wheels and cams and a method for manufacturing the same.
There are two types of transmissions, namely, mechanical type and fluid type. The former has such parts as gears, friction wheels and cams to convert the rotary or reciprocating motion of a shaft, crank or rod to a different motion.
It is desired that such parts be small, lightweight, less expensive, need no grease and consume less energy. To meet these requirements, such parts are often made from resins.
Among resins used for this purpose, resin materials known as super-engineering plastics, which are characterized by their high heat resistance, are especially desirable if the parts are used at high temperatures over 150.degree. C. There are two types of super-engineering plastics, i.e. thermosetting type and thermoplastic type. The former type includes polyimide (PI for short) resin and phenolic (PF) resin. The latter type includes polyarylether ketone (PAEK) resin, thermoplastic polyimide (TPI) resin, and polyamideimide (PAI) resin.
Among such super-engineering plastics, thermoplastic resins are more suitable in mechanical strength at low temperature and injection moldability for mass-production. As the main material for resin parts for mechanical transmissions, TPI resin, which has a glass transition point (Tg) of about 250.degree. C. and a heat resistance of 200.degree. C. or over, is particularly desirable because of its high mechanical strength in a wide temperature range and good injection moldability and mass-productivity.
But machine parts made by injection molding TPI resin have some drawbacks. One is that its crystallinity is as low as 4% or under. Low crystallinity means low wear resistance. Thus, such machine parts are not durable enough and poor in dimensional stability at high temperatures for use in mechanical transmissions.
When two of such TPI resin parts are brought into rolling, sliding or any other type of frictional contact with each other in a mechanical transmission, low wear resistance results from high cohesiveness. Thus, they tend to wear much more quickly than when a TPI resin part and a metal part are brought into frictional contact with each other under the same conditions.
An object of the invention is to provide machine parts which are made from TPI resin and can be used in a wide temperature range from lower than normal temperature to high temperature over 200.degree. C. and are still high in wear resistance and durability.
Another object of the invention is to provide machine parts that show high cohesive wear resistance and durability when they are brought into rolling, sliding or any other type of frictional contact with each other in a mechanical transmission.